JGJ/T 15-2008 in English

1 General Provisions
1.0.1 This standard is established in order to standardize the test methods of application of early estimating compressive strength of concrete, as well as realize use reliability and economic rationality.
1.0.2 This standard is applicable to the early estimating compressive strength of concrete, strength control in the concrete production and construction, as well as the aided design of concrete mix proportion adjustment.
1.0.3 Early estimating compressive strength of concrete shall not only meet the requirements of this standard, but also comply with those in the current relevant ones of the nation.
2 Terms and Symbols
2.1 Terms
2.1.1 Boiling water method
Shape concrete test piece, keep it still, cure it in boiling water, measure the compressive strength of accelerated curing concrete test piece, and then estimate the compressive strength of concrete cured for 28d under standard conditions.
2.1.2 Heated water method
Shape concrete test piece, keep it still, cure it in 80℃ heated water, measure the compressive strength of accelerated curing concrete test piece, and then estimate the compressive strength of concrete cured for 28d under standard conditions.
2.1.3 Warm water method
Shape concrete test piece, keep it still, cure it in 55℃ warm water, measure the compressive strength of accelerated curing concrete test piece, and then estimate the compressive strength of concrete cured for 28d under standard conditions.
2.1.4 Accelerated setting mortar method with high temperature and pressure curing
Sieve the mortar in concrete mixture, add setting accelerator, shape concrete test piece, cure it in high pressure and high temperature conditions, measure the compressive strength of accelerated curing mortar test piece, and then estimate the compressive strength of concrete cured for 28d under standard conditions.
2.1.5 Early ages method
Use the compressive strength of early age standard curing concrete to estimate the compressive strength of concrete cured for 28d under standard conditions.
2.1.6 Accelerated testing period
Time required from watering, mixing, sampling, shaping, accelerated curing to cooling.
2.2 Symbols
a, b--Regression coefficient;
fcu,i--Compressive strength value of ith group standard curing 28d concrete test piece;
--Compressive strength value of ith group accelerated curing concrete (mortar) test piece;
--Compressive strength value of accelerated curing concrete (mortar) test piece;
--Compressive strength estimating value of ith group standard curing 28d concrete;
--Compressive strength estimating value of standard curing 28d concrete;
mfcu--Compressive strength average value of n groups of standard curing 28d concrete test pieces;
n--Test piece group number;
r--Related coefficient of regression equation;
S*--Residual standard deviation of regression equation;
--Control target value of early estimating concrete strength standard deviation;
--Control target value of standard curing 28d concrete strength standard deviation;
--Standard deviation of early estimating concrete strength error.
3 Accelerated Curing Method of Concrete
3.1 Basic requirements
3.1.1 Before the accelerated curing of concrete test piece, water temperature in the accelerated curing box shall reach the specified requirements and the water temperature difference in the box shall not be greater than 2℃.
3.1.2 Water temperature in the accelerated curing box shall recover to the specified temperature within 15min after the test pieces are immersed in.
3.1.3 During the accelerated curing period, the temperature of curing water shall be measured and recorded continuously or at fixed time.
3.1.4 As for the accelerated curing box with thermostatic control device, the temperature of water shall also be checked by the thermometer or other temperature measuring device independent of thermostatic control device.
3.2 Accelerated curing equipment
3.2.1 Shape and dimension of accelerated curing box shall be determined according to the dimension, number and placed forms of test pieces in the box. At least 50mm gaps shall be reserved between test piece and box wall or between test pieces; the distance from test piece bottom surface to heat source shall not be less than 100mm. During the whole curing period, the water surface in the box and top surface of test piece shall maintain at least 50mm (see Figure 3.2.1).

Foreword i
1 General Provisions
2 Terms and Symbols
3 Accelerated Curing Method of Concrete
4 Accelerated Setting Mortar Method with High Temperature and Pressure Curing
5 Early Ages Method
6 Concrete Strength Relation Establishment and Strength Estimation
7 Application of Early Estimating Compressive Strength of Concrete
Appendix A Establishment Method of Concrete Strength Relation
Explanation of Wording in This Standard